Capacitive touch screens can be categorized into self-inductive capacitive ones and mutual inductive capacitive ones as per their detection mode of a touch signal. A mutual inductive capacitive touch screen comprises a plurality of drive lines and a plurality of sense lines intersecting the drive lines orthogonally, and mutual inductive capacitances are formed between the drive lines and the sense lines, where the capacitances at the locations where the drive lines and the sense lines overlap are not changeable by an outside touching object, and the mutual inductive capacitances formed by a fringe electric field generated at the locations where no electrodes overlap are influenced directly by an outside touching object.
The touch screen is scanned in the prior art as follows: a drive signal at a specific frequency is input line by line from one end of a drive line, and a signal at the same frequency is output from a sense line. When an object comes into contact with the surface of the touch screen, parasitic capacitances with a drive line and a sense line are formed, and a portion of the sense signal will leak to ground by the parasitic capacitances through a human body or the grounded object, so that the sense signal generated at that location will be attenuated, and therefore a specific location where a finger touches can be ascertained by detecting a signal change of the sense lines sequentially.
Typically, it is very likely for a finger to touch in a constantly moving way instead of touching at a point or in a defined area. Thus, when a drive signal is injected to each row sequentially in the vertical direction, that is, a scan line by line, there is a variable angle formed between the scan direction and a moving vector of a finger in a touch area. The amplitude and the profile of a gained touch signal will vary with this angle, and in the extreme case that the angle is equal to zero, there will be a special instance in which a scan pulse follows the moving finger. When the finger moves at a speed greater than or equal to a fast scan speed, there will even be a situation in which the moving touch signal fails to be followed and there is no output while there is a touch. Even if the scan speed is far above an instantaneous speed at which the finger goes across the surface of the display screen, there will be a different output signal arising from a different moving direction of the finger, thus resulting in a non-uniform touch signal. When there are a plurality of touch points at the same time, output signals of the different touch points may be different due to their relative distances and relative speeds to the spatial location of a drive signal, thus distorting the gained touch information. Consequently, when the touch screen is scanned, the precision of detecting the touching finger in motion may be low and the acquired information of the touching finger may not be comprehensive, thus making the scan inefficient.